Composite woods products may be described as falling into five classes, each characterized by the treatment of the wood within the product: plywood, oriented strandboard, particleboard, hardboard, and fiberboard. For each class of composite wood, the configuration of the wood contributes to that product's physical properties and typical application. In addition, the adhesive, the density of the wood, and additives such as resin or fire retardants, may change the characteristics of the product.
Most composite woods are made using a thermosetting or heat curing adhesive to bind or hold the cellulose wood fibers together during the process of manufacturing. Oriented strand board, for example, is made by the addition of adhesive to layers of shredded wood strands configured in certain orientations, followed by thermal pressing. Commonly used composite wood adhesive mixtures include resin binders of formaldehyde, urea-formaldehyde, melamine-formaldehyde, and isocyanate. Phenol-formaldehyde resins are typically used for manufacturing products that require some degree of durability under exterior exposure. Phenol may be condensed with formaldehyde to produce phenolic resins. Urea-formaldehyde resins are typically used in manufacturing products where dimensional uniformity and surface smoothness are of more concern than exterior durability (e.g., particleboard). Melamine-formaldehyde is an expensive resin used in decorative laminates or paper treatment. Isocyanates, such as di-phenylmethane di-isocyanate (or MDI) are also used in the manufacture of composite wood products. Natural adhesives, such as tannins, can be modified and reacted with formaldehyde to produce resins, as well. The curing characteristics of the resin, such as the cure temperature and time, are also additional factors to consider in the choice of resin. Urea- and phenol formaldehyde resins are most widely used in manufacturing composite wood products. Resin solids are generally mixed with a liquid vehicle or solvent, which acts as a carrier and a diluent.
Resin solids are expensive and may cause environmental and health problems. Oil shortages can cause further price increases. Formaldehyde is an irritant, a suspected carcinogen, and the resin base may release volatile organic compounds. (Toxicological Profile, ATSDR, DHHS-PHS 1999). Phenol formaldehyde or PF resin, being water proof and less expensive than other water proof resins, may be considered a leading resin or binder for shorthand reference herein.
An extender is a substance added to an adhesive mixture to serve an adhesive function, such as deeper adhesion in dense woods, tackier consistency, greater assembly time tolerance, etc. In the composite wood industry, flour is often used as an extender for these expensive resins. Extenders can reduce the overall cost of the adhesive mixture and the concentration of deleterious components that would otherwise compose a given volume of resin. Extenders may contribute to prepress tack and generally have some adhesive action or improvement to the final mixture, with the resin solids being the ultimate moisture resistant binder.
Extenders are often based on proteinaceous and amylaceous materials, and some of their desirable rheological properties may not be duplicated by more lignocellulosic-based materials. Flour extenders known in the field primarily include wheat flour, and also soy bean protein, casein, starch, oil cakes, corn flour, corn gluten protein, and seed gum. In some cases, wheat and other flours or materials may be mixed. The combination of gluten or protein and starch in wheat flour appears to aid in the adhesiveness or tack of the final mixture, making it one of the most widely used extenders. Yet wheat flour, although cheaper than resin, is still relatively expensive compared to many other natural alternatives. In use, wheat flour is also somewhat unpredictable or variable. The proteins in wheat flour can cause stringing and lumping of the adhesive mixture, and accumulation or build-up of glue on spray tips or other equipment, necessitating frequent cleaning. Thus, some have sought natural alternatives, such as fiber byproducts mixed with starch, but with limited commercial acceptance. It may generally be appreciated that a food product used as an extender will face economies different from those derived from a byproduct or process waste.
Extenders are often treated or modified to react with the resin to achieve adhesive performance, which can further increase the expense of the extender beyond the cost of materials. In some cases, the extender is treated so as to form a copolymer with the resin, or to enable the use of a reduced amount of phenol within an adhesive mixture, while still achieving a desired set of adhesive performance characteristics. While flour based extenders may be less expensive than PF resin, for example, they will carry at a minimum the market cost of the flour commodity and of any treatment steps.
In contrast, however, are additives referred to as fillers, which are generally non-adhesive compositions within the overall adhesive mixture. At the same time, though, fillers should not introduce adverse performance characteristics, such as unstable viscosities, poor spray-ability, or decreased adhesive strength. Some fillers are considered inert. In this way, materials that are suitable as fillers may be distinguished from materials suitable as extenders. As used herein, the term “filler” means a composition that is relatively non-adhesive and is added to an adhesive mixture to improve its working properties, permanence, strength, or other qualities. See, e.g., Sellers Jr., Terry, PLYWOOD AND ADHESIVE TECHNOLOGY 471 (1985). Fillers may also fill holes in a cracked or ruptured ply or veneer, decreasing porosity. Changes in economic or other factors, such as availability, mean that there is always a need for new or additional filler materials.
Accordingly, an object of the present approach is to provide a filler for use in composite wood products satisfactory to the performance and manufacturing needs, as well as a method for the production and use of such an adhesive or adhesive filler in the manufacture of composite wood products.
It is an object to accomplish the foregoing objective in a simple and cost effective manner.
Additional objects and advantages of embodiments will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be obtained by means of instrumentalities in combinations particularly pointed out in the appended claims.